Method for intermittently applying particulate powder to a fibrous substrate

ABSTRACT

A method for applying particulate powder material to a moving, pre-formed, fibrous substrate. In this method, particulate powder material is entrained in a continuous airstream. The air-entrained stream of particulate material exits a nozzle to be applied to the substrate or recirculated. The stream of air-entrained particulate matter has a velocity component in the direction of movement of the fibrous substrate.

This is a continuation of application Ser. No. 08/280,408, filed on Jul.26, 1994 now abandoned which is a continuation of application Ser. No.08/065,206, filed May 20, 1993 now abandoned which is a division ofapplication Ser. No. 806,954, filed Dec. 12, 1991, now U.S. Pat. No.5,213,817, issued May 25, 1993, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for fabricatinga fibrous pad containing a layer of powder therein, and moreparticularly, to a method and apparatus for intermittently sprayingparticulate powder material onto predetermined locations of a movingfibrous substrate to form a layer of particulate powder material withina predetermined portion of the fibrous substrate.

2. Description of the Prior Art

Hygenic articles such as disposable diapers, sanitary napkins,incontinence pads and sick bed sheets must have a high absorptioncapacity to effectively retain eliminated body fluids for acceptableperiods of time. Early hygenic articles of this type employed cellulosewadding, fluff cellulose or absorbent cotton as absorbent materials. Theproblem with these materials is that their absorbent capacity isrelatively small compared to their volume. In order to improve themoisture retaining capacity of hygenic articles made from thesematerials, the volume of such absorbent materials in the hygenic articlemust be increased. This produces a bulky product which is unacceptablein many hygenic articles, particularly sanitary napkins.

To reduce the volume and size of hygenic articles, and increase theirabsorbent capacity, highly absorbent materials have been developed andare combined within a fluid absorbent fibrous substrate composed ofcellulose fluff, wood pulp, textile fibers or other non-woven, fibrousmaterials. Such highly absorbent materials which have a high capacityfor absorbing water and body fluids are known in the art and generallyconsist of water insoluble, water-resisting organic polymers. Thesepolymers are partially or wholly synthetic and are commerciallyavailable in fine grain, particulate form.

Various techniques have been developed to distribute and locate thehighly absorbent material on or within the fibrous substrate. One priorart method of combining powder with a fibrous substrate comprisesapplying the powder to a top surface of the substrate. For example, U.S.Pat. No. 4,800,102 discloses a method and apparatus for spraying powderonto a fibrous substrate through a rotatable disc member having at leastone opening through which powders continuously sprayed from a sprayingmeans can reach the substrate. The apparatus also includes scraper meansdisposed above and closely adjacent to the disc member for deflectingpowder from the surface of the disc member through an opening. A lowerpowder receiving member is disposed beneath the scraper means forcollecting powder material deflected by the scraper means. An upperpowder sucker is disposed above the disc member adjacent the scrapermeans and is effective to remove from the disc member any powder whichis not forced by the scraper means through the opening. The powdermaterial recovered by the lower powder member and the upper sucker aretransported back to a powder supply. U.S. Pat. No. 4,861,405 alsodiscloses a method and apparatus for spraying powder to a top surface ofa laminated continuous sheet. The system of this patent utilizes thespeed of the continuous sheet to create an air flow zone of apredetermined thickness over a predetermined surface of the continuoussheet. Powder is continuously fed to the air zone by free fall through aconduit and by utilizing a decreasing-pressure phenomenon produced bythe air flow in which the pressure decreases as the predeterminedsurface of the laminated continuous sheet is approached. Powder iscaused to adhere to the predetermined surface as it is drawn toward thepredetermined surface of the laminated continuous sheet.

Another prior art method disclosed in U.S. Pat. No. 4,882,204 utilizesan aerosol spray nozzle of an aerosol container having absorbent powderparticles to form a diaper having highly absorbent material over theentire length and width of the diaper. The spray force drives many ofthe powder particles into subsurface layers of the diaper.

U.S. Pat. No. 4,675,209 discloses another prior art method for applyinghighly absorbent material onto a top surface of a moving substrate. Thismethod includes the steps of dispensing a melt adhesive film onprecisely defined areas of the substrate, covering such areas with theabsorbent material and then removing excess material which did notadhere to the adhesive coated areas.

Another prior art method of combining moisture absorbent material with afibrous substrate comprises intermixing highly moisture-absorbentmaterial with fibrous material in a forming chamber. U.S. Pat. No.4,927,346 discloses an apparatus for forming a non-woven pad consistingof fibrous material in which highly absorbent particles are intermixedwith fibrous material throughout a predetermined portion of thethickness of the pad. The non-woven pad is formed on top of a conveyormoving through a chamber which has a duct connected to a vacuum sourceoperable to draw fibrous material injected into the chamber onto theconveyor. A spray gun atop the conveyor discharges moisture absorbentmaterial at a predetermined velocity, such that the moisture absorbentmaterial is intermixed with the fibrous material throughout a centerlayer of the thickness of the non-woven pad while forming boundarylayers on either side of the center layer which are substantially freeof moisture absorbent material. The spray gun is operable intermittentlyto form spaced, sharply defined areas along the length and width of thenon-woven pad wherein each area has moisture absorbent materialinterspersed throughout a portion of the thickness thereof.

The conventional devices described above have problems associated withloss of moisture absorbent material through the conveyor in the formingchamber. In addition, the prior art methods which produce a substratehaving highly absorbent material throughout the entire length and/orwidth produces substantial waste because in subsequent formingoperations the non-woven pad is cut to the desired length of the hygenicarticle. Prior art methods which produce a substrate having theabsorbent material on a top surface have the disadvantage that themoisture absorbent capacity of the non-woven pad is substantiallylimited. This causes "gel blockage" wherein the moisture absorbentmaterial at the top of the pad becomes saturated with fluid and preventsthe transfer of moisture to the remaining portion of the pad. As aresult, the fluid is retained at the surface of the pad in contact withthe wearer of the hygenic article causing discomfort. Anotherdisadvantage with these methods is that the moisture absorbent materialis of a particulate or granular form and can be dislodged from the typeof pads which are not sealed at the ends.

Product specifications for present hygenic articles require highabsorbency material to be centrally located within a fibrous pad and itmay not extend to the edges or ends of the pad. In addition, theabsorbent material must be applied in a manner which does not damage orpass through the pad. Conventional devices and techniques, such as thosediscussed above, have not, however, been sufficiently capable ofefficiently producing a fibrous pad having particulate powder materialdistributed in a predetermined portion of the thickness, and across thelength and width, of the pad. In addition, the conventional formingtechniques have not been sufficiently able to deliver powder materialsin a substantially uniformly dispersed configuration that can be readilydirected and distributed into predetermined locations and patternswithin the fibrous pad.

SUMMARY OF THE INVENTION

The present invention is directed to a method and apparatus for applyingparticulate powder material to a moving fibrous substrate atpredetermined locations to form a layer of particulate material within apredetermined thickness of the substrate and over a predeterminedsurface of the substrate. The apparatus of the present inventionincludes a source of supply for the particulate powder material. Theparticulate powder material is transferred from the supply source to ahopper of a volumetric dry material feeder. The volumetric feederincludes a metering screw and nozzle shroud at its outlet to dischargean accurately metered quantity of particulate powder material to theoutlet of the volumetric feeder. Particulate powder material is thenpneumatically conveyed to a nozzle. The continuous stream of particulatepowder material flows through the nozzle and exits at an outlet thereof.The nozzle includes a stationary pivot mounted near its inlet and amovable pivot mounted near the center of the nozzle. The nozzle ismovable at a variable speed between a first position and a secondposition about the stationary pivot. A flow separator is disposedintermediate of the first and second positions beyond the outlet of thenozzle. The motion of the nozzle is controlled by a cam type driveconnected to the movable pivot.

The motion input to the cam type drive originates at a maker drive shaftwhich controls the rate of the moving fibrous substrate. An adjustabledifferential gear box is disposed between the maker drive shaft and anencoder to allow synchronizing the dispensing of the particulate powdermaterial at a predetermined location of the substrate. The encoder isdriven by a shaft of the gear box such that the encoder turns onerevolution per product cycle. A programmable controller communicateswith the output of the encoder and a servomotor. The servomotor isconnected to the movable pivot of the nozzle by a cam shaft. Theprogrammable controller drives the servomotor at a variable speed foreach product cycle.

The motion input to the nozzle causes the nozzle to oscillate betweenfirst and second positions such that the continuous stream ofparticulate material exiting the nozzle outlet is split into a first andsecond intermittent stream as the nozzle crosses the axis of the flowseparator. The first intermittent stream of particulate powder materialis applied to the moving fibrous substrate at a predetermined rate andat a predetermined location to form a layer of particulate powdermaterial within a predetermined portion of the thickness of the fibroussubstrate.

In an alternative embodiment of the present invention, recycle means areprovided to receive the second intermittent stream of particulate powdermaterial and pneumatically return it to the hopper of the volumetricfeeder. The recycle means includes a cyclone to separate the particulatepowder material from process air. The particulate powder material isdischarged from the cyclone through a rotary air lock and free fallsback into the hopper of the volumetric feeder.

The method and apparatus of the present invention allows an accuratelymetered quantity of particulate powder material to be applied to amoving fibrous substrate in a more precise manner than prior art methodsand apparatus. In addition, the use of recycle means lowers the amountof particulate powder material which is used for each product therebyleading to a lower raw material cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of the intermittent particulate powdermaterial dispensing apparatus of the present invention.

FIG. 2 is a schematic view of the volumetric feeder of the presentinvention.

FIG. 3 is an elevational view of the metering screw and nozzle shroud ofthe volumetric feeder of the present invention.

FIG. 4 is a schematic side view of the diverter nozzle and across-sectional side view of the diverter block of the presentinvention.

FIG. 5 is a schematic side view of the motion control for the diverternozzle in accordance with the method and apparatus of the presentinvention.

FIG. 6 is a graph of the servovelocity of the servomotor of the presentinvention for one product cycle.

FIG. 7 is a top view of a fibrous substrate having particulate powdermaterial at selected locations utilizing the method and apparatus of thepresent invention.

FIG. 8 is a cross-sectional view of the fibrous substrate of FIG. 4having particulate powder material within a predetermined portion of thethickness of the fibrous substrate.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, an apparatus 10 for intermittently dispensingparticulate powder material onto a moving fibrous substrate isillustrated. The apparatus 10 of the present invention can be used forparticulate powder materials such as sodium biocarbonate, highabsorbency polymers and other powders which are used in hygenic articlessuch as diapers, sanitary napkins and incontinence pads. The apparatus10 includes a source of supply 12 for the particulate powder material.The source of supply 12 can be a storage drum or any other suitablecontainer for storing particulate powder material. The source of supply12 has an outlet 14 which is adapted to receive a tube 16. The tube 16extends to the bottom of the source of supply. A drum unloader 18 isconnected to the source of supply 12 through tube 16. The drum unloader18 is a vacuum source and is operable to pneumatically transfer theparticulate powder material from the supply source 12 to a dump hopper20 of a volumetric dry material feeder 22. Automatic controls (notshown) on the drum unloader communicate with high and low sensorslocated within the dump hopper 20 and are operable to maintain the levelof particulate powder material in the dump hopper 20 between the highand low sensors. This system for maintaining the level of particulatepowder is conventional and well known in the art and any suitable systemfor maintaining said level may be employed.

Referring now to FIGS. 1, 2 and 3, the volumetric feeder 22 includes afeed hopper 24 located below the dump hopper 20. An example of avolumetric dry material feeder 22 which can be adapted to be used in thepresent invention is disclosed in U.S. Pat. No. 4,770,344 which ishereby incorporated by reference. The feeder 22 also includes externalmassaging paddles (not shown) to break bridges and condition theparticulate powder material into a uniform bulk density. Mounted withinthe base of the feed hopper 24 is a metering screw 26 and nozzle shroud27. The metering screw 26 is driven by a motor 28 at a predeterminedrate. The metering screw 26 is rotatable to discharge an accuratelymetered quantity of particulate powder material from the feed hopper 24through an outlet 30 formed within the base of feed hopper 24. Themetering screw 26 and nozzle shroud 27 are designed to improve theinstantaneous metering consistency of particulate powder materialdischarged through outlet 30. The outlet 30 is connected to a powderpump 32 which receives the accurately metered quantity of theparticulate powder material and entrains it within a stream of air fortransmittal through a flexible hose 34 connected to the outlet 30.

Turning now to FIG. 4, there is shown a diverter apparatus 36 whichincludes a nozzle 38 having an inlet 40 connected to the flexible hose34 for receiving the continuous stream of air-entrained particulatepowder material passing through hose 34. Nozzle 38 is a generallytubular snaped member having a hollow interior and tapers in an outlet42 which has a rectangular cross-section (not shown). The continuousstream of particulate powder material flows through nozzle 38 and exitsat outlet 42. The tapered shape of nozzle 38 and rectangularcross-section of outlet 42 combine to focus the shape of particulatepowder material exiting outlet 42 into a concentrated and well-definedcontinuous stream of powder material. A knife edge flow separator 41 isdisposed beyond the outlet 42 of nozzle 38. The flow separator 41 iswedge shaped having a wide end 43 and tapering to a narrow end 45. Theflow separator has a rectangular cross-section taken along a viewperpendicular to a plane of the separator 41. A stationary pivot 44 ismounted near the inlet 40. A cam shaft 46 is mounted near the center ofnozzle 38. The cam shaft 46 is connected to a disc 48 near its outeredge. The nozzle 38 is movable between a first position 47 and a secondposition 49 by a motion control applied to the cam shaft 46. As thenozzle 38 oscillates between the first and second positions 47 and 49,the continuous stream exiting at outlet 42 will be diverted into twointermittent streams of particulate powder material each time the nozzle38 crosses the plane of the flow separator 41. As an example of theformation of two intermittent streams in accordance with the method ofthe present invention, FIG. 4 shows a first intermittent stream ofparticulate powder material 51 and a second intermittent stream ofparticulate powder material 53 formed as nozzle 38 moves from 47 to 49to 47 to 49 to the plane of flow separator 41.

Referring now to FIGS. 1 and 4, a conveyor 50 is located below thenozzle 38. The conveyor 50 is passed over cylindrical rollers 52 and 54,of which the driving roller 54 is driven by a motor (not shown) at apredetermined rate. The motor includes a drive shaft 56 which rotates atthe predetermined rate. An elongated fibrous substrate 58 is placed onthe conveyor and moves in the direction shown by the arrows. As will bedescribed in more detail below, the first intermittent stream ofparticulate powder material 51 is applied to a predetermined location ofthe moving substrate 58.

In an alternative embodiment of the present invention, a recycleapparatus 60 can be utilized. The recycle apparatus 60 includes adiverter block 62 having a rectangular inlet 64 for receiving the secondintermittent stream of particulate powder material 53. Thecross-sectional length of the inlet 64 is preferably at least as long asthe cross-sectional length of nozzle outlet 42 in order to allow theentire second intermittent stream 53 to flow into inlet 64. A pump 66 isused to pneumatically convey the second stream of particulate powdermaterial 53 through a tube 67 to a cyclone 68. The cyclone 68 separatesthe particulate powder material from the process air used to convey thesecond stream of powder material. The particulate powder material isthen discharged from cyclone 68 through a rotary air lock 70 and freefalls back into the dump hopper 20 of the volumetric feeder 22.

Referring now to FIG. 5 there is shown a schematic diagram of the motioncontrol for the diverter nozzle 38. The motion input to nozzle 38originates at the maker drive shaft 56. The maker drive shaft 56 isconnected to an adjustable differential gear box 72 at a first shaft 74by a belt 76. An encoder 78 is connected to the differential gear box 72at a second shaft 80. The differential gear box 75 is adjustable suchthat the encoder 78 turns one revolution per product cycle. This allowssynchronizing the dispensing of particulate powder material at apredetermined location of the fibrous substrate 58. The encoder 78produces an output 79 which is received by a programmable controller 82.The controller 82 communicates with a servomotor 84 which has a shaft 86connected to disc 48. The controller 82 drives the servomotor 84 suchthat its shaft 86 has a variable speed profile over one product cycle asshown in FIG. 6. In addition, the variable speed profile of servomotor84 will cycle at the predetermined rate of the maker drive shaft 56.

In operation, conveyor 50 having the fibrous substrate 58 thereon ismoving at a predetermined rate. At the same time, an accurately meteredcontinuous stream of particulate powder material is being dischargedthrough the outlet 42 of nozzle 38. The nozzle 38 is being moved betweenthe first and second positions 47 and 49 according to the variable speedprofile of servomotor 84 by cam shaft 46 and is cycling at thepredetermined rate. As an illustrative example, the nozzle 38 may beginfrom first position 47, corresponding to position A of the variablespeed profile of servomotor 84, and quickly reaches the narrow end 45 ofthe separator 41 corresponding to position B. Up to this point,particulate powder material flows into the inlet 64 of diverter block62. As the nozzle 38 quickly crosses the plane of the separator 41 themotion of the nozzle 38 slows down due to the variable speed ofservomotor 84, reaches the second position 49 corresponding to positionC and begins to return to the narrow end 45 of separator 41corresponding to position D. During this period, particulate powdermaterial is applied to the fibrous substrate 58 at a predeterminedlocation to form a layer of particulate powder material within apredetermined portion of the thickness of the fibrous substrate 58. Thenozzle 38 then quickly returns to its first position 47 corresponding toposition E. For each product this cycle repeats itself. Typically, thepresent invention operates at 600 product cycles per minute.

The diverter nozzle 38 is preferably angled in the direction of movementof the fibrous substrate 58 to give the particulate powder material avelocity component in the same direction as the moving substrate 58 inorder to reduce "splashing" of particulate powder material off thesubstrate 58. The wedge shaped separator combined with the fast motionof nozzle 38 when it crosses the plane of separator 41 produce a cleancut-off of particulate powder material flow each time the nozzle 38crosses the plane of separator 41. This allows the diverter apparatus 36to generate well defined first and second intermittent streams ofparticulate powder material.

As shown in FIG. 7, the result of the method and apparatus of thepresent invention is a fibrous substrate 58 having particulate powdermaterial 88 at selected areas 89 along the fibrous substrate 58. In afurther step of fabricating a final hygenic article, the substrate 58 iscut along cut lines 90 to form individual fibrous pads 91. In addition,as shown in FIG. 8, the velocity of the first intermittent stream ofparticulate powder material applied to the substrate 58 is chosen suchthat a layer 92 of particulate powder material 88 forms within apredetermined portion of a thickness of each fibrous pad 91.

In accordance with current specifications for hygenic articles, themethod and apparatus of the present invention allows the powder 88 to becentrally located and does not extend to the edges or ends of eachindividual pad 91. The width of powder material pattern 89 is determinedby the length of the rectangular cross-section of outlet 42 of nozzle38. The use of controller 82 to control the motion of nozzle 38 via aservomotor 84 permits "tuning" the discharge profile of particulatepowder material and quickly changing the length of the pattern 89 byselecting an appropriate control program for controller 82. For example,if the servo velocity is constant over each product cycle the patternlength will be less than the length of pattern 89. On the other hand, ifthe servovelocity is increased near the beginning and end of each cycle,or the servovelocity is decreased at the middle of each cycle, this willresult in a longer pattern than the length of pattern 89. The length ofeach individual pad 91 can be lengthened or shortened by adjusting thedifferential gear box 72. The length of an individual pad 91 isdetermined by the number of revolution that the maker drive shaft 56makes for each product cycle. To lengthen or shorten the length ofpattern 89, the gear box 72 is adjustable such that the encoder 78 turnsone revolution over a wide range of revolutions of the maker drive shaft56.

The present invention provides for a method and apparatus for applyingan accurately metered quantity of particulate powder material to amoving fibrous substrate. In addition, the use of recycle means torecapture particulate powder material on the recycle side of the flowseparator leads to a lower range of powder usage, translating to a lowerraw material cost. Typically, the apparatus of the present inventionutilizes an average flow of 0.15 grams of particulate powder materialper product cycle.

While the invention has been particularly shown and described withrespect to preferred embodiments thereof, it will be understood by thoseskilled in the art that the foregoing and other changes in form anddetails may be made therein without departing from the spirit and scopeof the invention, which should be limited only by the scope of theappended claims.

What is claimed is:
 1. A method of applying particulate powder materialto a pre-formed fibrous substrate comprising the steps of:moving saidpre-formed fibrous substrate in a horizontal path; establishing a supplyof particulate powder material in a feed hopper; feeding a meteredquantity of particulate powder material into an outlet of the feedhopper; forming a continuous air-entrained stream of particulate powdermaterial at said outlet of said feed hopper and transporting saidcontinuous air-entrained stream through a nozzle for ejection onto saidfibrous substrate; separating said continuous air-entrained stream ofparticulate powder material exiting said nozzle into a first and asecond intermittent air-entrained stream of particulate powder materialsuch that said first intermittent air-entrained stream of particulatepowder material is applied to said moving pre-formed fibrous substrateat a predetermined location of said pre-formed fibrous substrate to forma layer of particulate powder material within a predetermined portion ofsaid pre-formed fibrous substrate; wherein said continuous stream ofair-entrained particulate powder material exiting said nozzle isdirected along a flow direction which has a velocity component in thedirection of said moving pre-formed fibrous substrate.
 2. The method ofclaim 1 wherein said layer of particulate powder material is formedwithin a predetermined portion of a thickness of said pre-formed fibroussubstrate.
 3. The method of claim 1 further comprising the step ofreturning said second intermittent air-entrained stream of particulatematerial to said supply of particulate material.
 4. The method of claim1 wherein said separating step comprises:providing a flow separatorbeyond an outlet of said nozzle and intermediate of a first and a secondnozzle position; and oscillating said nozzle at a variable speed betweensaid first and second positions such that said flow separator separatessaid continuous air-entrained stream of particulate powder materialexiting said nozzle into first and second intermittent air-entrainedstreams as the nozzle crosses a plane of said flow separator.